Automatic air conditioner system with variable displacement compressor for automotive vehicles

ABSTRACT

An automatic air conditioning system for automotive vehicles with a variable displacement compressor comprises a sensor for detecting an intake air temperature of air flowing through an evaporator placed just behind the evaporator, a control valve for essentially changing the discharge volume of the compressor on the basis of the difference between the intake air temperature and its target value, and a CPU for deriving the different target values in response to two modes, namely a BI-LEVEL mode wherein conditioned air is simultaneously discharged from both upper and lower discharge outlets, and a MONO-LEVEL mode wherein conditioned air is discharged from either the upper or lower discharge outlets. The control valve operates in such a manner that, when the difference is plus, that is, the intake air temperature is higher than the target value, the discharge volume is essentially increased, and when the difference is minus, that is, the intake air temperature is lower than the target value, the discharge volume is essentially decreased. Thus, in the BI-LEVEL mode the amount of air reheated by a heater unit becomes larger than the amount of reheated air in the MONO-LEVEL mode. According to the invention, the BI-LEVEL mode effect can be sufficiently satisfied, particalarly, in a fuel-saving mode wherein the difference between the intake air temperature and the temperature of air to be discharged from the discharge outlets is very small.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an automatic air conditioning systemwith a variable displacement compressor for automotive vehicles,particularly to an automatic air conditioning system with a variabledisplacement compressor for automotive vehicles, in which a temperatureof conditioned air flowing through a lower discharge outlet, such as afoot vent, can be controlled at a higher temperature than a temperatureof air flowing through another discharge outlet, such as a chest vent,in a BI-LEVEL mode in which two discharge outlets are simultaneouslyopened, and particularly in BI-LEVEL mode and fuel-saving mode in whichthe compressor is driven at a low speed and the discharge of refrigeranttherefrom is relatively low.

2. Description of the Prior Disclosure

Recently, there have been proposed and developed various automatic airconditioning systems with a control unit which controls opening angle ofdoors, such as a switchable fresh/recirculation air intake door, an airmixing door, a defroster door, a chest vent door, a foot vent door, orthe like, and controls the amount of air flowing through the evaporatorof the air conditioning system in response to output signals fromvarious sensors for detecting various physical quantities, such as anambient temperature, room temperature in the vehicular cabin, magnitudeof insolation, intake air temperature of the evaporator, suctionpressure of the compressor, and in response to output signals indicativeof ON/OFF state of various switches, such as an air conditioner switch,a blower switch, an ignition switch, a defroster switch, or so forth. Ingeneral, in a fuel-saving mode, such an automatic air conditioningsystem controls the compressor in such a manner that the discharge ofthe compressor is cut off at a low level, thereby resulting in thelowering of torque absorbed by the compressor. Therefore, it is requiredthat a temperature of air flowing through the evaporator, which will bereferred to as an "intake air temperature" is controlled so as not tobecome lower than the desired temperature. Conventionally, the intakeair temperature is measured just behind the evaporator. In fuel-savingmode, it is not desirable that the cooled air flowing through theevaporator is reheated by the heater unit, for the reason of thewasteful consumption of a larger torque than actually necessary. In aconventional air conditioning system, in fuel-saving mode, the intakeair temperature is so controlled as to be close to a target temperatureof air to be discharged from discharge outlets, which will be referredto as a "target discharge air temperature". The target discharge airtemperature is calculated by the CPU of the automatic air conditioningsystem on the basis of the various control parameters, such as a presettemperature manually input through a control panel mounted on aninstrument panel of a vehicle, an ambient temperature detected by anambient sensor, magnitude of insolation detected by an insolationsensor, room temperature in a vehicular cabin detected by a roomtemperature sensor. Therefore, in the fuel-saving mode, the air flowingthrough the evaporator is directly introduced through an air mixing doorinto an air mixing chamber because the air mixing door is so controlledas to be positioned in a fully closed position in which the air flowingthrough the evaporator is not introduced into the heater unit with theresult that the air flowing through the evaporator is not partiallyreheated by the heater unit. Therefore, in the BI-LEVEL mode and thefuel-saving mode, a temperature of air discharged through an upperdischarge outlet, such as a chest vent, and a defroster, is essentiallyequal to a temperature of air discharged through a lower dischargeoutlet, such as a foot vent, because the air flowing through theevaporator is not partially reheated by the heater unit. A feature ofthe BI-LEVEL mode is that conditioned air of two different temperaturesis discharged through two different discharge outlets. In other words,in BI-LEVEL mode, the temperature of conditioned air flowing through thefoot vent must be higher than that flowing through the chest vent or thedefroster nozzle. However, in the prior art air conditioning system, theaforementioned effect of the BI-LEVEL mode is not satisfied in thefuel-saving mode.

SUMMARY OF THE INVENTION

It is, therefore in the view of the above disadvantages, an object ofthe present invention to provide an automatic air conditioning systemwith a variable displacement compressor for automotive vehicles, inwhich a temperature of conditioned air flowing through a lower dischargeoutlet, such as a foot vent, can be controlled to a higher value than atemperature of air flowing through another discharge outlet, such as achest vent, in BI-LEVEL mode in which two discharge outlets aresimultaneously opened, and particularly in BI-LEVEL mode and fuel-savingmode in which the compressor is driven at minimum requirements and thedischarge of refrigerant therefrom is relatively low.

It is another object of the invention to provide an automatic airconditioning system with a variable displacement compressor forautomotive vehicles, which is capable of finely controlling thedischarge of the compressor in response to the BI-LEVEL mode and inother modes in which only a single discharge outlet is opened.

In order to accomplish the aforementioned and other objects, anautomatic air conditioning system for automotive vehicles with avariable displacement compressor comprises first detecting means fordetecting an intake air temperature, defined by a temperature of airflowing through an evaporator of the air conditioning system as measuredjust behind the evaporator, discharge changing means for essentiallychanging the discharge volume of refrigerant discharged from thecompressor on the basis of the difference between the intake airtemperature and its target value, mode signal generating means forgenerating a mode signal representing whether the air conditioningsystem is operated in a first mode wherein conditioned air issimultaneously discharged from both upper and lower discharge outlets oris operated in a second mode wherein conditioned air is discharged fromeither the upper or lower discharge outlets, and target value derivingmeans for deriving the target value of the intake air temperature on thebasis of the mode signal in such a manner that the target value in thefirst mode is smaller than the target value in the second mode. Thedischarge changing means operates in such a manner that, when the intakeair temperature is higher than the target value, the discharge volume isessentially increased, and when the intake air temperature is lower thanthe target value, the discharge volume is essentially decreased. Theautomatic air conditioning system further comprises second detectingmeans for detecting a physical quantity indicative of environmentalconditions in and around the automotive vehicle, and calculating meansfor calculating a target discharge air temperature, discharged from thedischarge outlets, on the basis of the physical quantity and a presettemperature input from temperature setting means for setting a desirableroom temperature in the vehicular cabin. The physical quantity isambient temperature, magnitude of insolation, and/or room temperature inthe vehicular cabin. The target value deriving means selects theappropriate target value of the intake air temperature in considerationof the target discharge air temperature.

According to another aspect of the invention, an automatic airconditioning system for automotive vehicles comprises discharge meansfor compressing and discharging refrigerant, discharge changing meansfor changing discharge volume of the refrigerant discharged from thedischarge means, mode signal generating means for generating a modesignal representing whether the air conditioning system is operated in afirst mode wherein conditioned air is simultaneously discharged fromboth upper and lower discharge outlets or is operated in a second modewherein conditioned air is discharged from either the upper or lowerdischarge outlets, first detecting means for detecting an intake airtemperature defined by a temperature of air flowing through anevaporator of the air conditioning system placed just behind theevaporator, second detecting means for detecting a physical quantityindicative of environmental conditions in and around the automotivevehicle, calculating means for calculating a target discharge airtemperature, to be discharged from the discharge outlets, on the basisof the physical quantity and a preset temperature input from temperaturesetting means for setting a desirable room temperature in the vehicularcabin, target value deriving means for deriving an individual targetvalue of the intake air temperature in accordance with the targetdischarge air temperature in such a manner that the target value in thefirst mode is smaller than the target value in the second mode, andcontrol means capable of controlling the discharge changing means on thebasis of the difference between the intake air temperature and thetarget value in such a manner that, when the target value is lower thanthe intake air temperature, the discharge volume of the dischargingmeans is essentially increased depending on the difference, and whensaid target value is higher than the intake air temperature, thedischarge of the discharging means is essentially decreased depending onthe difference.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a system diagram illustrating the main components of anautomatic air conditioning system for automotive vehicles according tothe invention.

FIG. 2 is a longitudinal sectional view illustrating the preferredembodiment of a variable displacement compressor according to theinvention.

FIG. 2A is a sectional view illustrating the preferred embodiment of acontrol valve for the variable displacement compressor under a conditionwherein suction pressure of the compressor exceeds a preset pressure.

FIG. 2B is a sectional view illustrating the preferred embodiment of thecontrol valve of the variable displacement compressor under a conditionwherein a suction pressure of the compressor is equal to or lower than apreset pressure.

FIG. 3 is a detailed sectional view illustrating the internalconstruction of the preferred embodiment of a control valve according tothe invention.

FIG. 4 is a block diagram illustrating the control circuit controllingrespective components of an automatic air conditioning system accordingto the invention.

FIG. 5 is a flow chart representative of a basic program to control anautomatic air conditioning system according to the invention.

FIG. 6 is a flow chart representative of a program for controlling thevariable displacement compressor according to the invention.

FIG. 6A is a state transition graph illustrating two states of theengine speed of an automotive vehicle.

FIG. 7 is a flow chart representative of a program for quick coolingcontrolling the automatic air conditioning system according to theinvention.

FIG. 7A is a graph illustrating the relationship between an intake airtemperature of the evaporator and the elapsed time, during the quickcooling operation.

FIG. 8 is a flow chart representative of a program for controlling thesolenoid current supplied to an electromagnetic solenoid which is usedfor changing the preset pressure of the control valve of the compressoraccording to the invention.

FIGS. 8A and 8B are graphs used for deriving the solenoid current on thebasis of the difference between an actual intake air temperature of theevaporator and a target intake air temperature.

FIG. 9 is a flow chart representative of a program for controlling aplurality of pistons within the compressor under a small strokecondition, when the engine is driven at a high revolutions or theautomotive vehicle is under acceleration.

FIG. 10 is a flow chart representative of a program for controlling theopening angle of the air mixing door of an automatic air conditioningsystem according to the invention.

FIG. 11 is a flow chart representative of a program for controlling thecompressor of the invention under fuel-saving and power-savingconditions.

FIG. 11A is two graphs for deriving a target intake air temperature froma target discharge air temperature, the graphs are associated with StepsS7152 and S7153.

FIG. 12 is a flow chart representative of a program for controlling thecompressor under maximal dehumidification conditions.

FIG. 13 is a flow chart representative of a program for controlling thecompressor under the low-temperature DEMIST mode wherein a defrosterdoor and a foot vent door are open and a chest vent door is closed.

FIG. 13A is a graph illustrating the relationship between two targetrefrigerant temperatures and two preset times for causing pulsation ofthe compressor during the low-temperature DEMIST mode shown in FIG. 13.

FIG. 14 is a flow chart representative of a program for controlling thesolenoid current during the low-temperature DEMIST mode so as to changethe preset pressure of the control valve of the compressor according tothe invention.

FIGS. 14A and 14B are graphs used for deriving the solenoid current onthe basis of the difference between a refrigerant temperature and atarget refrigerant temperature.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 1 to 14B, particularly to FIG. 1, the preferredembodiment of an automatic air conditioning system for automotivevehicles comprises a compression/refrigerating cycle type of cooler unit100 having a variable displacement compressor 2 which is driven by anengine 1, a condenser 3, an evaporator 4, a liquid tank 5, and anexpansion valve 6. The variable displacement compressor 2 dischargeslarger refrigerant volumes only when the suction pressure Ps exceeds thepreset pressure Pr. The preset pressure Pr is controlled by a solenoidcurrent I_(SOL) provided from a control unit 40 shown in FIG. 4 asmentioned below.

On the other hand, the evaporator 4 is provided in an air conditioningduct 7 which has a fresh air inlet 7a and a recirculation air inlet 7b.A fresh/recirculation switching air intake door 8 is mounted on theinner wall of the duct 7 for controlling the amount of air flowingthrough each of the inlets 7a and 7b. In the duct 7, as is generallyknown, provided are a blower 9, a heater unit 10, and an air mixing door11. Furthermore, the duct 7 has a chest vent 7c, a foot vent 7d, and adefroster nozzle 7e. The air-flows through the chest vent 7c, the footvent 7d, and the defroster nozzle 7e are respectively controlled by achest vent door 12, a foot vent door 13, and a defroster door 14 whichare mounted on the inner wall of the duct 7. Although it is not shown inFIG. 1, for simplification of the drawing, these doors, namely the airintake door 8, the air mixing door 11, the chest vent door 12, the footvent door 13, and the defroster door 14 are driven by means of aplurality of actuators shown in FIG. 4, namely an air intake dooractuator 50, an air mixing door actuator 51, a chest vent door actuator52, a foot vent door actuator 53, and a defroster door actuator 54.

The variable displacement compressor 2 will be described in detail byFIGS. 2, 2A, 2B, and 3. As clearly shown in FIG. 2, in this embodiment,a swash plate type of variable displacement compressor 2 is used for thecooling unit 100. The swash plate 25 is provided in a casing chamber 21Rof a casing 21 of the compressor 2 for controlling the discharge of thecompressor 2 in such a manner that, when the suction pressure Ps isintroduced into the casing chamber 21R, the slope angle of the swashplate 25 becomes higher, or when the discharge pressure Pd is introducedinto the casing chamber 21R, the slope angle of the swash plate becomeslower.

As shown in FIG. 2, a rotational shaft 24 is provided in the casing 21of the compressor 2. The rotational shaft 24 is rotated through a pulley23 by way of a belt 22 which is driven by the engine 1. The swash plate25 is fixed obliquely to the axis of rotation of the rotational shaft24. A non-rotary wobble 26 engages with the swash plate 25 through ajournal 25a of the swash plate 25. A piston 28 which slidinglyreciprocates within a cylinder chamber formed in a cylinder block 27, isconnected through a piston rod 29 to the non-rotary wobble 26 in such amanner that the piston 28 is rotatably connected to a first ball joint29A of the piston rod 29 and the non-rotary wobble 26 is rotatablyconnected to a second ball joint 29B of the piston rod 28. When theswash plate 25 rotates with the rotational shaft 24, the second balljoint 29B reciprocates along the substantially axial direction of thepiston 28 in accordance with the oscillating movement of the non-rotarywobble 26 with the result that the piston 28 reciprocates along the axisthereof. In accordance with the reciprocation of the piston 28,refrigerant is sucked via a suction chamber 30s, through a suctionopening 35s and is discharged through a discharge opening 35d into adischarge chamber 30d such that, in FIG. 2, the refrigerant is suckedvia the suction chamber 30s according to the right-hand directionalmovement of the piston and it is discharged into the discharge chamber30d according to the left-hand directional movement of the piston.Although it is not shown in FIG. 2, these openings 35s and 35d aresuitably opened and closed according to the reciprocation of the piston28 by way of valve means which are provided at the openings 35s and 35d.Although only one piston 28 is shown in FIG. 2, the variabledisplacement type of compressor 2 is essentially a multiple-cylindertype of compressor in which a plurality of pistons 28 are connected tothe corresponding plurality of piston rods 29, each second ball joint29B being arranged at regular interval on the circumference of thenon-rotary wobble 26. In this manner, the refrigerant under highpressure is fed from the compressor 2 to the condenser 3.

As best shown in FIG. 2A, when the suction pressure Ps is introducedinto the casing chamber 21R, the slope angle of the swish plate 25becomes higher, and as shown in FIG. 2B, when the discharge pressure Pdis introduced into the casing chamber 21R, the slope angle of the swashplate 25 becomes lower. In order to selectively communicate the casingchamber 21R with either the suction chamber 30s or the discharge chamber30d, the variable displacement type of compressor 2 has a control valve32 in an end cover 31 thereof. The construction of the control valve 32will be described in detail by FIG. 3.

As shown in FIG. 3, the control valve 32 has a substantially cylindricalvalve body 322 which sealingly engages a substantially cylindrical valveseat 321 at the top end thereof such that the valve seat 321 insertedinto the valve body 322 under press fit. A valve pin 324 is slidablyinserted in the cylindrical valve body 322 in such a manner that theaxis of the former is consistent with that of the latter. A ball 323 isfixed on the top end of the valve pin 324 within the valve seat 321 foropening or closing the lower opening 321b of the valve seat 321. Theball 323 is normally urged downwardly in the axial direction of thevalve pin 324 by means of a conical spring 325 such that the sphericalsurface of the ball 323 abuts the ball seat 326. A high-pressure chamber328 is defined by the space between the inner wall of the end cover andthe top end of the valve seat 321. The high-pressure chamber 328communicates through the port 327 with the suction chamber 30d andfurther the high-pressure chamber 328 communicates via the upper opening321a of the valve seat 321 through the lower opening 321b of the valveseat 321 with an inner chamber 330. The inner chamber 330 communicatesvia a port 329A which is formed in the valve body 322 through a secondport 329B which is formed in the end cover 31, with the casing chamber21R. As set forth above, the ball 323 functions as a valve so as toestablish or prevent the communication between the high-pressure chamber328 and the inner chamber 330. As seen in FIG. 3, the inner peripheralsurface of valve body 322 sealingly mates the outer peripheral surfaceof the valve pin 324 at the substantially intermediate portion of thevalve body 322.

On the other hand, an end cap 332 is mounted on the lower end of thevalve body 322 in an air-tight fashion such that the inner peripheralsurface of the end cap 332 hermetically mates the bottom surface of thevalve body 322. The end cap 332 includes a bellows 331 therein. An endmember 334 is hermetically provided on the top end of the bellows 331 inan air-tight fashion, while a spring seat 333 is disposed on the lowerend of the bellows 331. A compression spring 335 is provided between theinner wall of the end member 334 and the spring seat 333 in such amanner that the bellows 331 is normally stretched in the longitudinaldirection thereof by spring force. Furthermore, a center rod 336 extendsfrom the cylindrical hollow of the spring seat 333 through the centeropening of the end member 334 to the bottom end portion of the valve pin324 in the substantially axial direction of the valve pin 324. Acuspidal top end of the center rod 336 mates the bore which is formed atthe bottom end of the valve pin 324. The center rod 336 is firmly fixedto the inner surface of the end member 334 at the point adjacent to thecuspidal top end thereof. On the other hand, the frusto-conical lowerend of the center rod 336 is slidably inserted into the cylindricalhollow of the spring seat 333. In this construction, only the relativedistance between the frusto-conical lower end of the center rod 336 andthe spring seat 333 is changed according to the expansion andcontraction of the bellows 331.

A control chamber 339 is defined by the space between the bellows 331and the end cap 332. The control chamber 339 communicates through ports337 and 338, which are respectively formed in the end cap 332 and theend cover 31, with the suction chamber 30s. The control chamber 339communicates through the flow passage defined by the space between asubstantially frusto-conical valve seat 343 and a substantiallyfrusto-conical valve portion 340 with an intermediate chamber 341 of thevalve body 322. The intermediate chamber 341 communicates, through aport 342 formed in the end cover 31, with the casing chamber 21R.

As best seen in FIG. 3, a movable disc plate 344 is firmly fixed throughthe bottom face of the bellows 331 on the bottom end of the spring seat333. A plunger 344A of an electromagnetic solenoid 345 is connected tothe movable disc plate 344 such that the axis of the plunger 344A isessentially consistent with that of the center rod 336. A return spring346 is arranged between the bottom face of the end cap 332 and theperimeter of the movable disc plate 344 and in a manner to surround thesolenoid 345 for normally biasing the movable plate 344 toward thebottom surface of the spring seat 333. The spring constant of the returnspring 346 is set sufficiently higher than that of the compressionspring 335. The electromagnetic solenoid 345 is connected through arelay 56 to a output circuit 49 as shown in FIG. 4. The stroke of theplunger 344A is controlled by a solenoid electric current I_(SOL) asmentioned below.

When the suction pressure Ps of the compressor 2 exceeds the presetpressure Pr which is mainly determined by the internal pressure withinthe bellows 331 and the spring constant of the compression spring 335,the bellows 331 is contracted against the spring force caused by thespring 335 with the result that the center rod 336 moves downward. Thevalve pin 324 moves downward along with the center rod 336 due to thespring force caused by the conical spring 325. Under this condition, themovable plate 344 does not move, while the ball 323 abuts the ball seat326 and simultaneously the valve portion 340 moves away from the valveseat 343. This condition of the higher suction pressure Ps than thepreset pressure Pr is shown in FIGS. 2A and 3. As clearly seen in FIG.2A, the suction pressure Ps is introduced from the control chamber 339through the port 342 to the casing chamber 21R, via the intermediatechamber 341, thereby causing higher slope angle of the swash plate 25.As a result, the discharge of the compressor 2 is increased.

Conversely, when the suction pressure Ps is equal to or lower than thepreset pressure Pr, the center rod 336 moves upward by the spring forceof the spring 335 with the result that the valve pin 324 is pushed up.As a result, the ball 323 moves away from the ball seat 326 and whilethe valve portion 340 sealingly mates the valve seat 343. Under thiscondition as well, the movable plate 344 does not move. This conditionof the lower suction pressure Ps of than the preset pressure Pr is shownin FIG. 2B. As clearly shown in FIG. 2B, the discharge pressure Pd isintroduced from the high-pressure chamber 328 through the inner chamber330 via the ports 329A and 329B to the casing chamber 21R, therebycausing lower slope angle of the swash plate 25. As a result, thedischarge of the compressor 2 is decreased.

Consequently, such a variable displacement compressor controls the slopeangle of the swash plate on the basis of the difference of pressurebetween the cylinder chamber and the casing chamber, that is, thedifference of pressure before and behind the pistons.

One such swash plate type of variable displacement compressor has beendisclosed in the U.S. Pat. No. 4,428,718 entitled "VARIABLE DISPLACEMENTCOMPRESSOR CONTROL VALVE ARRANGEMENT" said patent was granted on Jan.31, 1984 and assigned to the assignee "GENERAL MOTORS CORPORATION". Thedisclosure of the above-identified U.S. Patent is herein incorporated byreference for the sake of disclosure.

In accordance with the invention, the above mentioned preset pressure Prof the variable displacement compressor can be changed as follows.

When the electromagnetic solenoid 345 is demagnetized, the movable plate344 is positioned at a point where the compression spring 335 balanceswith the return spring 346. This point will be hereinafter referred toas a "balancing point". The position of the movable plate 344 movesupward away from the balancing point in a manner essentiallyproportional to an increase in the solenoid current I_(SOL) with theresult that the preset pressure Pr is increased in a manner essentiallyproportional to an increase in the solenoid current I_(SOL).

FIG. 4 shows a control circuit 40 for the preferred embodiment of theautomotive automatic air conditioning system according to the presentinvention. The control circuit 40 compresses a central processing unit(CPU) 41 which is connected through an input circuit 42 to an ambienttemperature sensor 43 for detecting an ambient temperature T_(AMB), aroom temperature sensor 44 for detecting temperature T_(INC) in thevehicular cabin, an insolation sensor 45 for detecting magnitude of theinsolation Q_(SUN), an intake air temperature sensor 46 for detectingtemperature T_(INT) of air flowing just downstream of the evaporator 4,a refrigerant temperature sensor 47 being provided in the outlet of theexpansion valve 6 for detecting refrigerant temperature T_(ref), a watertemperature sensor 48 for detecting temperature T_(W) of cooling waterfor cooling the engine 1. Furthermore, the input circuit 42 is connectedto an air conditioner switch 57, a blower switch 58, an ignition switch59, a defroster switch 60, an intake pressure sensor 61 for detecting anintake manifold pressure, an engine speed sensor 62 for detecting enginespeed, and an air mixing door opening angle sensor (air mix door anglesensor) 63 for detecting an opening angle of the air mixing door 11.

The CPU 41 is connected through an output circuit 49 to an air intakedoor actuator 50, an air mixing door actuator 51, a chest vent dooractuator 52, a foot vent door actuator 53, a defroster door actuator 54,and a blower control circuit 55 which is connected to the blower motor9. The output circuit 49 is also connected through a relay 56 to anelectromagnetic solenoid 345 mounted in the aforementioned control valve32.

In this construction, the CPU 41 controls suitably the actuators 50 and54 and the solenoid 345 in such a manner that the CPU changes theopening angle in each door and controls magnitude of electric current tobe supplied to the solenoid 345 on the basis of the information inputthrough the input circuit 42 from the sensors 43 to 48, the sensors 61to 63, and the switches 57 to 60. In other words, the CPU suitablycontrols the amount of air to be discharged through each door, thetemperature of air to be discharged through each door, and the presetpressure Pr of the control valve 32. The CPU further controls the blowermotor 9 by means of the blower control circuit 55 in response to anair-flow signal which is indicative of the amount of air to bedischarged from the blower fan. This air-flow signal is determined bythe CPU 41 on the basis of the signals from the air mixing door openingangle sensor 63 and the intake air temperature sensor 46 according tothe conventional method of the prior art automotive automatic airconditioning systems.

This control unit 40 for the air conditioning system of the inventionwill be operated in accordance with the order of steps of a flow chartshown in FIG. 5.

In Step 10 (S10), in which the automatic air conditioning system isautomatically operated by the control unit 40, the memorized values inthe CPU 41 are initialized to predetermined values. For example, apreset temperature T_(PTC) is initialized to a predeterminedtemperature, such as, for example "25° C.".

In Step 20 (S20), the CPU 41 receives the information T_(AMB), T_(INC),Q_(SUN), T_(INT), T_(ref), and T_(W) through the input circuit 42 fromthe respective sensors, namely the ambient temperature sensor 43, theroom temperature sensor 44, the insolation sensor 45, the intake airtemperature sensor 46, the refrigerant temperature sensor 47, and thewater temperature sensor 48. In Step S20, the CPU 41 further receivesthe desired preset temperature T_(PTC) input by a passenger through acontrol panel (not shown). Therefore, the automatic air conditioningsystem is automatically operated depending on the desired presettemperature.

In Step 30 (S30), the CPU compensates the ambient temperature T_(AMB)input from the sensor 43 to a value T_(AM), which is in close proximityto the actual ambient temperature, in consideration of thermal effectdue to other heat sources, such as a condenser, a radiator, and thelike.

In Step 40 (S40), the CPU converts the insolation information input froman insulator sensor, such as a photodiode, to the heating valueQ'_(SUN).

In Step 50 (S50), the CPU compensates the preset temperature T_(PTC) onthe basis of the compensated ambient temperature T_(AM).

In Step 60, the CPU calculates a target discharge air temperature T_(O)on the basis of the compensated preset temperature T'_(PTC), the roomtemperature T_(INC), the compensated ambient temperature T_(AM), and theinsolation Q'_(SUN) and further calculates an opening angle of the airmixing door 11 on the basis of the difference between the targetdischarge air temperature T_(O) and the actual discharge airtemperature. The actual discharge air temperature is derived on thebasis of the intake air temperature T_(INT) and a present opening angleX of the air mixing door 11 input from the air mixing door opening anglesensor 63. The control procedure of the opening angle of the air mixingdoor 11 will be hereinbelow detailed in accordance with the flow chartin FIG. 10.

In Step 70 (S70), the compressor 2 is controlled by the CPU. The controlprocedure of the compressor 2 will be hereinbelow described in detailaccording to the flow chart in FIG. 6.

In Step 80 (S80), the CPU controls the opening angle of each of thedoors 12, 13, and 14 through which conditioned air is discharged intothe vehicular cabin.

In Step 90 (S90), the CPU controls the air intake door 8 for selectivelyswitching as to whether the intake air is introduced through the freshair inlet 7a or through the recirculation air inlet 7b.

In Step 100 (S100), the CPU controls the speed of the blower 9 foradjusting the amount of air to be discharged through the doors 12, 13and 14.

FIG. 6 shows a flow chart for controlling the compressor 2 according tothe present invention at Step S70 of FIG. 5.

The compressor control routine begins at Step 700 (S700) and thenproceeds to Step 701 (S701) at which a test is made to determine whethera blower is ON or OFF in response to the input signal from the blowerswitch 58. If the answer to Step S701 is in the negative (no), thecompressor 2 is stopped at Step 702 (S702). If the answer to Step S701is in the affirmative (yes), the Step 703 (S703) proceeds to testwhether the refrigerant temperature T_(ref) is within a first state or asecond state as shown in the state transition graph at Step S703 and thediscriminated state of the refrigerant temperature T_(ref) is stored ina predetermined first memory in the CPU. Accordingly to the transitiongraph of Step S703, it is required that the refrigerant temperatureT_(ref) exceeds the predetermined temperature T_(ref2), for example 0°C. so as to transit from the second state to the first state.Conversely, it is required that the refrigerant temperature T_(ref)becomes lower than the predetermined refrigerant temperature T_(ref1),for example -15° C. so as to transit from the first state to the secondstate. In other words, the difference between the temperatures T_(ref1)and T_(ref2) corresponds to a hysteresis for preventing the compressor 2from frequently starting or switching OFF. The refrigerant temperatureT_(ref) lying in the first state means that thermal load is relativelyhigh. Conversely, the refrigerant temperature T_(ref) lying in thesecond state means that thermal load is relatively low, such as thewintertime. In Step S 704, if the refrigerant temperature T_(ref) is inthe second state, Step S702 proceeds and, as noted previously, thecompressor 2 is stopped. In Step S704, if the refrigerant temperatureT_(ref) is in the first state, Step 705 (S705) proceeds in which a testis made to determine on the basis of the input signal from the enginespeed sensor 62 whether, according to FIG. 6A, the engine output R_(rev)is at a high-revolution state or at a low-revolution state. As set forthabove, the difference between these engine speeds R_(rev1), for example,4,500 r.p.m. and R_(rev2), for example 5,000 r.p.m. corresponds to ahysteresis through which the state of engine output changes from alow-rev. state to a high-rev. state or vice versa. For example, in orderto change from the low-rev. state to the high-rev. state, it is requiredthat the engine exceeds the revolution R_(rev2). In Step S705, if theengine output R_(rev) is in the low-rev. state, Step 706 (S706) isentered in which a test is made to discriminate whether the compensatedambient temperature T_(AM) is in a third state, a fourth state, or afifth state. After this, the discriminated state of the ambienttemperature T_(AM) is stored in a predetermined second memory in theCPU. As set forth above, the difference between a predeterminedtemperature T_(AM1), for example -5° C. and a predetermined temperatureT_(AM2), for example -2° C. corresponds to a hysteresis for transitionbetween the fourth state and the fifth state. Likewise, the differencebetween a predetermined temperature T_(AM3), for example 5° C. and apredetermined temperature T_(AM4), for example 8° C. corresponds to ahysteresis for transition between the third state and the fourth state.

In Step S705, if the engine speed R_(rev) is in the high-speed state,Step 712 (S712) is entered in which the variable displacement compressor2 is so controlled as to operate under small stroke condition of theplurality of the pistons 28, thereby causing relatively small dischargefrom the compressor 2. Therefore, the compressor 2 can be driven at arelatively low torque and as a result torque absorbed by the compressor2 is relatively small. The control of the compressor 2 as executed inStep S712 will be hereinafter referred to as a "destroke control".

In Step 707 (S707), a test is made to determine whether the defrosterswitch 60 is ON. If the answer to Step S707 is in the negative (no),Step 708 (S708) proceeds in which a test is made to determine whetherthe target discharge air temperature T_(O) calculated at the Step S60 ofFIG. 5 is lower than a temperature T_(rcd), for example -10° C. at whichthe air mixing door 11 is operated in a fully closed position in whichthe air mixing door 11 shunts all of the air to flow into the heaterunit 10. If the answer to Step S708 is in the affirmative (yes), Step709 (S709) proceeds in which the compressor 2 is operated under a quickcooling condition. The control of the compressor 2 as shown in Step S709will be hereinafter referred to as a "quick cool-down control". StepS708 is executed once when the ignition switch 59 is changed from an OFFstate to an ON state or the blower switch 58 is changed from an OFFstate to an ON state.

As described below, the "quick cool-down control" will be executed inaccordance with the flow chart in FIG. 7. The "quick cool-down control"routine begins at Step 7090 (S7090) and then at Step 7091 (S7091) atarget intake air temperature T'_(INT), which represents a targettemperature of air flowing through the evaporator 4 at an outlet of theevaporator 4, is set to a predetermined temperature T₁, for example 0°C. and a timer TIMER1 is set to a predetermined time t₁ which is lessthan the time required to freeze the evaporator. In this manner, in the"quick cool-down control" according to the invention, the target intakeair temperature T'_(INT) can be set to a temperature T₁ lower than theaforementioned "freezing start possible temperature" T₄, for example 3°C. The reason for this low target temperature setting is for situations,when ambient air temperature is excessively high, for example during thesummer daytime hours. Due to the preset time interval TIMER1, theevaporator 4 never freezes, even if the actual intake air temperatureT_(INT) is set to the temperature T₁ lower than the "freezing startpossible temperature" T₄. This is experimentally assured by theinventors of the invention.

In Step 7092 (S7092), an electric current I_(SOL1) to be supplied to thesolenoid 345 is calculated and then the solenoid current I_(SOL1) issupplied through the relay 56 to the solenoid 345 based on thecalculated value.

The solenoid current I_(SOL1) control in Step S7092, will be executedaccording to thee flow chart in FIG. 8. The solenoid current controlroutine begins at Step 940 (S940) and then at Step 941 (S941), thedifference (T_(INT) -T'_(INT)) between the intake air temperatureT_(INT) and the target intake air temperature T'_(INT) is calculated.Next, in Step 942 (S942), a first electric current I_(P) and a secondelectric current I_(I) are respectively derived in accordance with thegraphs in FIGS. 8A and 8B based on the difference (T_(INT) -T'_(INT)).The first electric current I_(P) is directly read from the graph of FIG.8A. On the other hand, the second electric current I_(I) is calculatedin a manner to add an additional electric current ΔI_(I), which isderived from the graph of FIG. 8B, to the present second electriccurrent I_(I) and as a result the second current I_(I) is renewed to thesecond current I_(I) +ΔI_(I). In FIGS. 8A and 8B, the values of currentI₁ and I₂, and the values of temperature T₂, and T₃ are respectively,for example 0.98 mA, 0.8 A, 6° C., and 20° C. and these values areexperimentally determined so as to suitably operate the solenoid 345.Subsequently, in Step 943 (S943), the solenoid current I_(SOL1) isfinally calculated as the difference (I_(P) -I_(I)) between the firstelectric current I_(P) and the renewed second electric current I_(I). Inthe above mentioned solenoid current control, the unit of the first andsecond electric currents are respectively "A" and "mA". As will beappreciated from the above, magnitude of the solenoid current I_(SOL1)is mainly determined by the first electric current I_(P) and is slightlycompensated by the second electric current I_(I). In this way, thesolenoid current I_(SOL1) is finely controlled according to theprocedure of FIG. 8. In FIGS. 8A and 8B, when the difference (T_(INT)-T'_(INT)) is equal to "0", the solenoid current I_(SOL1) is equal tothe difference (I₂ -I_(I)) between the first current I₂ and the secondcurrent I_(I). Under application of the solenoid current (I₂ -I_(I)),the movable plate 344 is positioned in a particular position upward ofthe above mentioned "balancing point". This position of the movableplate 344 will be referred to as an "initial position". When the movableplate is positioned in the "initial position", a particular presetpressure Pr is defined. This particular preset pressure will be referredto as an "initial preset pressure". In this preferred embodiment, the"initial preset pressure" is set to the particular preset pressure basedon the "freezing start possible temperature" T₄. Therefore, if theintake air temperature T_(INT) is equal to the temperature T₄ (T_(INT)=T₄), the initial preset pressure is held because the solenoid currentI_(SOL1) is not changed. If the intake air temperature T_(INT) is higherthan the temperature T₄ (T_(INT) >T₄), the initial preset pressure isdecreased according to decrease in the solenoid current I_(SOL1).Further, if the intake air temperature T_(INT) is lower than thetemperature T₄ (T_(INT) <T₄), the preset pressure is increased accordingto increase in the solenoid current I_(SOL1).

After the solenoid current control in Step S7092 of FIG. 7, Step 7093(S7093) proceeds in which a test is made to determine whether the intakeair temperature T_(INT) is equal to the "freezing start possibletemperature" T₄. If the answer to Step S7093 is in the negative (no),the routine returns from Step S7093 to Step S7092 and thus Steps 7092and 7093 are repeated until the answer to Step S7093 becomes affirmative(yes). If the answer to Step S7093 is in the affirmative, that is,T_(INT) =T₄, Step 7094 (S7094) proceeds in which the timer TIMER1starts.

In Step 7095 (S7095), the solenoid current I_(SOL1) is controlled inaccordance with the same solenoid current control routine shown in FIG.8 as Step S7092.

In Step 7096 (S7096), a test is made to determine whether the targetdischarge air temperature T_(O) is higher than a predeterminedtemperature T₅, for example 8° C. at which the air mixing door 11 startsto move from the closed position to the open position for supplying theair passing through the evaporator 4 into the heater unit 10. If theanswer to Step S7096 is in the affirmative (yes), Step 7098 (S7098)proceeds in which the target intake air temperature T'_(INT) isincremented by 1° C./sec. If the answer to Step S7096 is in the negative(no), Step 7097 (S7097) proceeds in which a test is made to determinewhether the preset time t₁ of the timer TIMER1 has elapsed. If theanswer to Step 7097 is in the negative (no), the routine returns fromStep S7097 to Step S7095. If the answer to Step 7097 is in theaffirmative (yes), Step S7098 proceeds. After Step S7098, the procedurereturns from the "quick cool-down control" routine to Step S80 of FIG.5.

As will be appreciated from FIGS. 8, 8A, and 8B, during the "quickcool-down control" as shown in FIG. 7, the magnitude of the solenoidcurrent I_(SOL1) is quickly decreased until the intake air temperatureT_(INT) of the evaporator 4 reaches through the "freezing start possibletemperature" T₄ to the temperature T₁. Under this condition, the movableplate 344 moves downward, thereby causing the lowering of the presetpressure Pr. As a result, since the state as shown in FIG. 2A at whichthe suction pressure Ps is higher than the preset pressure Pr, issatisfied even if the suction pressure Ps is relatively low, the largeslope angle of the swash plate 25 of the compressor 2 is maintained.That is to say, the discharge of the compressor 2 is kept at a highlevel, thereby maintaining optimal cooling power during the quickcool-down control.

As clearly seen from FIGS. 7 and 7A, the "quick cool-down control" ofthe compressor 2 is continued until the target discharge air temperatureT_(O) is higher than the temperature T₅ or until the preset time t₁elapses from a time when the intake air temperature T_(INT) hasdecreased to the temperature T₄ after setting the target intake airtemperature T'_(INT) to the predetermined temperature T₁. In thismanner, the compressor 2 is driven for the predetermined time intervalst₁ at conditions of maximal discharge during the "quick cool-downcontrol".

In Step S708 of FIG. 6, if the answer is in the negative, that is, thetarget discharge air temperature T_(O) is equal to or higher than thetemperature Trcd, Step (S710) proceeds in which a test is made todetermine whether the vehicle is under acceleration based on an intakemanifold pressure P_(INT) detected by the intake pressure sensor 61. Ifthe answer to Step 710 is in the affirmative (yes), Step 711 proceeds inwhich a test is made to determine whether the intake air temperatureT_(INT) of the evaporator 4 is lower than a predetermined temperatureT_(INT1), for example 5° C. If the answer to Step 711 is in theaffirmative (yes), Step 712 (S712) proceeds in which the aforementioned"destroke control" is executed.

As shown in FIG. 9, the "destroke control" begins at Step 7120 (S7120)and then Step 7121 (S7121) proceeds in which a test is made to determinewhether the intake air temperature T_(INT) is higher than thetemperature (T'_(INT) +1). As this target intake air temperatureT'_(INT), derived is the final preset value of the target intake airtemperature T'_(INT) in a previously executed compressor control, eitherof all of four compressor controls, namely the aforementioned "quickcool-down control", three compressor controls as described below,"fuel-saving and power-saving control", "maximal dehumidificationcontrol", and "low-temperature DEMIST control". In Step S7121, in otherwords, a test is made to discriminate if the intake air temperatureT_(INT) is too close to the target intake air temperature T'_(INT). Ifthe answer to Step 7121 is in the negative (no), Step 7122 (S7122)proceeds in which the target discharge air temperature T'_(INT) isincremented by a predetermined temperature T₁₀, for example 5° C. andthen Step 7124 (S7124) proceeds in which the above mentioned solenoidcurrent control as shown in FIGS. 8, 8A, and 8B is executed. If theanswer to Step S7121 is in the affirmative (yes), Step 7123 (S7123)proceeds in which the target discharge air temperature T'_(INT) is setto a predetermined temperature T₁₁, for example 20° C. which temperatureT₁₁ is higher than the temperature T₁₀ and then Step S7124 proceeds. Inthis way, the solenoid 345 is operated according to the value of thesolenoid current I_(SOL1) calculated at Step S7124. After this, theprocedure returns from Step S7124 to Step S80 of FIG. 5.

A negative answer at Step S7121 means that the intake air temperatureT_(INT) is excessively close to the target intake air temperatureT'_(INT). Therefore, in Step S7122, even though the target intake airtemperature T_(INT) is incremented by the relatively low temperatureT₁₀, the value of the solenoid current I_(SOL1) becomes higher. Due tothis high solenoid current, the removable plate 344 moves upward and asa result the preset pressure Pr of the control valve 32 is increased.Therefore, since the state as shown in FIG. 2B at which the suctionpressure Ps is equal to or lower than the preset pressure Pr, issatisfied even if the suction pressure Ps is relatively high, the smallslope angle of the swash plate 25 of the compressor 2 is maintained.That is to say, the discharge of the compressor 2 is kept at a lowlevel, thereby causing lower cooling power from the cooling unit 100.

On the other hand, a positive answer at Step S7121 means that the intakeair temperature T_(INT) is lower than the predetermined temperatureT_(INT1) but not in excessively close proximity to the target intake airtemperature T'INT. Therefore, in Step S7123, the target intake airtemperature T'_(INT) of the evaporator 4 is set to a higher temperatureT₁₁ than the temperature T₁₀ such that acceleration performance isincreased even if the cooling power is lowered. In this manner, the highsolenoid current I_(SOL1) is applied to the solenoid 345, and as aresult the movable plate 344 moves upward, thereby causing increase inthe preset pressure Pr of the control valve 32. Since the target intakeair temperature T'_(INT) in Step S7123 is set to a sufficiently hightemperature T₁₁ than that in Step S7122 with the result that the presetpressure Pr in Step S7123 is set higher than that in Step S7122.Therefore, since the state as shown in FIG. 2B is satisfied even if thesuction pressure Ps is high, the small slope angle of the swash plate 25is kept. The predetermined temperature T₁₁ used at Step S7123corresponds to the temperature of air flowing through the evaporator 4as measured just behind the evaporator 4, under this particularcondition the compressor 2 never stops but is driven with the minimumdischarge. In practice, the temperature T₁₁ is experimentallydetermined.

When the target intake air temperature T'_(INT) is increased in StepsS7122 or S7123, the actual detected intake air temperature T_(INT)gradually increases. Therefore, since the difference S between thetarget discharge air temperature T_(O) and the actual discharge airtemperature is changed, and air mixing door 11 is actuated to the closedposition such that air flowing to the heater unit 10 is cut of. As aresult, the discharge air temperature is maintained at a substantiallyconstant value even though the flow of refrigerant is decreased, thatis, the discharge of the compressor 2 is small.

The opening angle of the air mixing door 11 is controlled in accordancewith FIG. 10. The control routine of the opening angle of the air mixingdoor 11 begins at Step 600 (S600) and then at Step 601 (S601) aplurality of constants A, B, C, D, E, F, and G are respectivelyinitialized to predetermined values as used for the equation of Step 603(S603) in FIG. 10. These values A to G are experimentally determined inconsideration of vehicular sizes or vehicular shapes.

In Step 602 (S602), a signal indicative of a present opening angle X ofthe air mixing door 11 is input from the air mixing door opening anglesensor 63.

Next, in Step 603 (S603), the difference S between the target dischargeair temperature T_(O) and the actual discharge air temperature isderived in accordance with the equation shown in Step S603. In thisequation, the front term "(A+D)T'_(PTC) +BT_(AM) +CQ'_(SUN) -DT_(INC)+E" corresponds to the target discharge temperature T_(O), while therear term "(FX+G)(82-T_(INT))+T_(INT) " corresponds to the actualdischarge air temperature. As will be appreciated from the equation, thetarget discharge air temperature T_(O) is calculated on the basis of theabove mentioned values T'_(PCT), T_(AM), Q'_(SUN), and T_(INT).Furthermore, the actual discharge air temperature is calculated on thebasis of the intake air temperature T_(INT) and the opening angle X ofthe air mixing door 11.

Subsequently, at Step 604 (S604),the difference S is compared with apredetermined value S_(O), for instance 2° C. If the difference S issmaller than the value -S_(O), Step 605 (S605) proceeds in which the airmixing door 11 is activated by the air mixing door actuator 51 to aclosed direction in such a manner that the amount of air flowing throughthe heater unit 10 is decreased. The closed direction of the air mixingdoor 11 will be hereinafter referred to as a "cold direction". If theabsolute value |S| of the difference S is equal to or smaller than thevalue +S_(O), Step 606 (S606) proceeds in which the opening angle of theair mixing door 11 is held as it is. If the difference S is larger than-S_(O), Step 607 (S607) proceeds in which the air mixing door 11 isactivated by the air mixing door actuator 51 to an open direction insuch a manner that the amount of air flowing through the heater unit 10is increased. The open direction of the air mixing door 11 will behereinafter referred to as a "hot direction". In this manner, the airmixing door 11 is continuously controlled on the basis of theabove-mentioned control parameters T'_(PTC), T_(Am), Q'_(SUN), T_(INC),T_(INT), and X in accordance with the flow chart of FIG. 10.

As will be seen from FIG. 6, the "destroke control" of Step S712 isexecuted under a particular condition in which the engine 1 is driven ata higher output than the revolution R_(rev2), for example 5,000 r.p.m.or the automotive vehicle is under acceleration.

The "destroke control" will be featured as follows:

In the "destroke control" under acceleration conditions of vehicle, isexecuted when the procedure shown in FIG. 6 advances from Step S710 viaStep S711 to Step S712. Since the intake air temperature T_(INT) islower than the predetermined temperature T_(INT1), for example 5° C.,the task of the cooling unit 100 is considerably accomplished.Therefore, a feature of this "destroke control" is that the coolingpower of the cooling unit 100 is lowered so as to smoothly acceleratethe automotive vehicle. That is, the preset pressure Pr of thecompressor 2 is set at a relatively high level with the result thattorque absorbed by the compressor 2 is lowered. In this "destrokecontrol" under acceleration conditions, if the intake air temperatureT_(INT) is in close proximity to the target intake air temperatureT'_(INT), and thus the cooling task of the evaporator 4 is fullyaccomplished, the preset pressure Pr of the control valve 32 is set to arelatively high pressure in such a manner to add the predeterminedtemperature T₁₀ to the target intake air pressure T'_(INT) as shown inStep S7122 of FIG. 9. Therefore, the cooling power of the cooling unit100 is lowered and as a result torque absorbed by the compressor 2decreases. Thus, the acceleration performance of the automotive vehicleis increased.

On the other hand, if the intake air temperature T_(INT) is not in closeproximity to the target intake air temperature T'_(INT) but the intakeair temperature T_(INT) is lower than the predetermined temperatureT_(INT1), and thus the cooling task of the cooling unit 100 is fullyaccomplished, the preset pressure Pr of the control valve 32 is set to aconsiderably higher pressure in such a manner to replace thepredetermined temperature T₁₁ to the target intake air temperatureT'_(INT) as shown in Step S7123 of FIG. 9. Therefore, the cooling powerof the cooling unit 100 is considerably lowered and as a result torqueabsorbed by the compressor 2 considerably decreases. Thus, theacceleration performance of the automotive vehicle is considerablyincreased. That is to say, when compared the "destroke control" executedthrough Step S7123 with the "destroke control" executed through StepS7122, the former (S7123) is different from the latter (S7122) at apoint where the acceleration performance of the former exceeds that ofthe latter.

In the "destroke control" during a high-output state of the engine 1,which is executed when the procedure shown in FIG. 6 advances directlyfrom Step S705 to Step S712, since the engine 1 is in the highrevolution state, the compressor 2 is also driven through the pulley 23by the belt 22 at a high speed. Therefore, a feature of this "destrokecontrol" is that the compressor 2, when driven at a high speed, causesthe plurality of pistons 28 to reciprocate with a relatively smallstroke to prevent the durability of the compressor 2 from decreasing.That is, the slope angle of the swash plate 25 of the compressor 2 isset at a small value with the result that the life of the compressor 2becomes long particularly due to a decrease in abrasion of the pistons.

Again, in FIG. 6, if the answer to Step S711 is in the negative (no),Step 713 (S713) proceeds in which a test is made to determine whether anair conditioner switch is in the On state. If the answer to Step S713 isin the affirmative (yes), the procedure jumps from Step S713 to Step 716(S716). Conversely, if the answer to Step S713 is in the negative (no),Step 714 (S714) proceeds in which a test is made to determine whetherthe aforementioned ambient temperature T_(AM) is in the third, fourth,or fifth states. If the answer to Step S714 is the fourth or fifthstates, the procedure jumps to Step S702 in which the compressor 2 isstopped. If the answer to Step S714 is the third state, Step 715 (S715)proceeds in which the compressor 2 is so controlled as to save powerthereof in order to avoid wasteful consumption of fuel. This control ofthe compressor 2 will be hereinafter referred to as a "fuel-saving andpower-saving control".

The "fuel-saving and power-saving control" will be described in detailin accordance with a flow chart of FIG. 11.

This "fuel-saving and power-saving control" routine begins at Step 7150(S7150) and then Step 7151 (S7151) proceeds in which a test is made todetermine whether the air conditioning system is operated in BI-LEVELmode wherein the chest vent door 12 and the foot vent door 13 are openedand the defroster door 14 is closed and the proportion between therespective amounts of air flowing through the chest vent 7c and the footvent door 7d is substantially equal. If the answer to Step S7151 is inthe affirmative (yes), Step 7152 (S7152) proceeds in which the targetintake air temperature T'_(INT) is derived on the basis of the targetdischarge air temperature T_(O) in accordance with a lower graph IIhaving a second characteristic as shown in FIG. 11A. If the answer toStep S7151 is in the negative (no), Step 7153 (S7153) proceeds in whichthe target intake air temperature T'_(INT) is derived on the basis ofthe target discharge air temperature T_(O) in accordance with an uppergraph I having a first characteristic as shown in FIG. 11A.

In Step 7154 (S7154), a test is made to discriminate whether the intakeair temperature T_(INT) is in a sixth state or a seventh state accordingto a state transition graph of Step S7154. In the state transition graphof Step S7154, the difference in temperature between a predeterminedtemperature T₆, for example 1.5° C. and the "freezing start possibletemperature" T₄ corresponds to a hysteresis which is provided forpreventing the compressor 2 from frequently starting or switching OFF.

In Step 7155 (S7155), a test is made to determine whether thetemperature T_(INT) is in the seventh state. If the answer to Step S7155is in the affirmative, that is, the seventh state, Step 7157 (S7157)proceeds in which the compressor 2 is stopped. On the other hand, if theanswer to Step S7155 is in the negative, that is, the sixth state, Step7156 (S7156) proceeds in which the aforementioned control of thesolenoid current I_(SOL1) is executed according to FIG. 8. After this,the procedure returns from Steps S7156 or S7517 to Step S80 of FIG. 5.

In FIG. 11A, the respective temperatures denoted by reference numeralsT₇, T₀₁, T₀₂, T₀₃, and T₀₄ are experimentally determined depending uponthe various sizes and/or types of automotive vehicles. For example,these temperatures T₇, T₀₁, T₀₂, T₀₃, and T₀₄ may be 15° C., 8° C., 18°C., 20° C. and 30° C., respectively.

As will be clearly seen from FIG. 11A, the target intake air temperatureT'_(INT) is set on the basis of the target discharge air temperatureT_(O), thereby allowing the compressor a fine degree of control.

As is well known, since prior art automatic air conditioning systemsconventionally control an opening angle of an air mixing door on thebasis of the difference between an actual intake air temperature T_(INT)and a target discharge air temperature T_(O) for providing a desireddischarge air temperature, the intake air temperature T_(INT) becomesundesirably lower due to fluctuation of engine speed. Under thiscondition, conventional automotive air conditioning systems control theair mixing door to its open or hot direction with the result that thedischarge air temperature reaches the target discharge air temperature.In this system, the compressor consumes more torque than desired,thereby causing wasteful fuel consumption.

On the other hand, in the present embodiment according to the invention,the air conditioning system controls the compressor 2 in such a mannerthat the discharge of the compressor 2 is finely controlled on the basisof the target intake air temperature T'_(INT) finely selected accordingto two graphs shown in FIG. 11A. As a result, the intake air temperatureT_(INT) is controlled by regulating the discharge of the compressor 2.Therefore, in the automatic air conditioning system of the presentinvention, the intake air temperature T_(INT) does not become lower thanthe desired intake air temperature, unlike prior art automatic airconditioning systems. That is to say, to avoid the undesirable loweringof the intake air temperature T_(INT), the present automatic airconditioning system selects the target intake air temperature T'_(INT)on the basis of the temperature relationship between the target intakeair temperature T'_(INT) and the target discharge temperature T_(O)whose relationship has been experimentally determined and thendetermines the solenoid current I_(SOL1) in accordance with theprocedure of FIG. 8. In this manner, the compressor 2 is driven atminimum requirements, thereby allowing the compressor 2 to save powerthereof in order to avoid wasteful consumption of fuel.

In the "fuel-saving and power-saving control" of the embodimentaccording to the invention, since the compressor 2 is driven at minimumrequirements, the intake air temperature T_(INT) of the evaporator 4tends to be in close proximity to the target discharge air temperatureT_(O). For this reason, the air mixing door 11 tends to be operated inthe fully closed or cold position wherein a flow passage for the heaterunit 10 is fully closed and the air flowing through the evaporator 4does not enter into the heater unit 10 at all. Under this condition, ifthe air conditioning system is operated in the BI-LEVEL mode, thedischarge air temperature of the foot vent 7d is substantially equal tothat of the chest vent 7c. The reason for this is that the air mixingdoor is fully closed. Therefore, conditioned air having essentially sametemperature is discharged from both vents in spite of the conventionalarrangement of the automotive air conditioner system, in which the footvent is arranged nearer the heater unit than other discharge outlets,such as the chest vent, and the defroster nozzle. As is well known, theBI-LEVEL mode is an operating condition where the discharge airtemperature of the foot vent is higher than that of the chest vent. Asset forth above, in the "fuel-saving and power-saving control" , theBI-LEVEL mode is not sufficiently satisfied. Therefore, the "fuel-savingand power-saving control" of the preferred embodiment provides the twographs I and II having respectively the first and second characteristicsas shown in FIG. 11A. As clearly seen in the lower graph of FIG. 11A, inBI-LEVEL mode, the intake air temperature T_(INT) relative to theidentical target discharge air temperature T_(O) is set to a lower valuethan another modes except the BI-LEVEL mode with the result that thedischarge air temperature of the foot vent is higher than that of thechest vent and thus the BI-LEVEL mode is satisfied. While, using the"fuel-saving and power-saving control" during BI-LEVEL operation, thefuel and power-saving effect becomes slightly lowered.

That is to say, when comparing the "fuel-saving and power-savingcontrol" function during the BI-LEVEL mode with same during modes otherthan the BI-LEVEL mode, the solenoid current I_(SOL1) of the former isset to a lower value than that of the latter on the basis of therespective target intake air temperatures I'_(INT) relative to theidentical target discharge air temperature T_(O), thereby allowing thetarget intake air temperature T'_(INT) of the former to be assigned alower value than in the latter operation. As a result, the air mixingdoor 11 moves to the hot direction slightly. In this way, during theBI-LEVEL mode, the "fuel-saving and power-saving control" is executed.

On the other hand, in FIG. 6, if the answer to Step S707 is in theaffirmative (the defroster switch 60 is in an On state), Step 716 (S716)proceeds in which a test is made to determine whether the state of theambient temperature T_(AM) stored in Step S706 is in the third, fourth,or fifth states. If the ambient temperature T_(AM) is in the thirdstate, Step 717 (S717) proceeds in which a dehumidification control asshown in detail in FIG. 12, which control will be hereinafter referredto as a "maximal dehumidification control", is executed as follows.

The "maximal dehumidification control" begins at Step 7170 (S7170), andthen Step 7171 (S7171) proceeds in which the target intake airtemperature T_(INT) is set to the "freezing start possible temperature"T₄, for example 3° C.

In Step 7172 (S7172), a test is made to discriminate whether the intakeair temperature T_(INT) is in the sixth state or the seventh state, bothstates being shown in Step S7154 of FIG. 11.

In Step 7173 (S7173), a test is made to determine whether the intake airtemperature T_(INT) is in the seventh state. If the answer to Step S7173is in the affirmative, Step 7174 (S7174) proceeds in which thecompressor 2 is stopped. Conversely, If the answer to Step S7173 is inthe negative, Step 7175 (S7175) proceeds in which the solenoid currentI_(SOL1) is controlled according to FIG. 8 as set forth above. Afterthis, the procedure returns from Steps S7174 or S7175, to Step S80 ofFIG. 5.

On the other hand, in Step S716 of FIG. 6, if the ambient temperatureT_(AM) is in the fourth state, Step 718 (S718) proceeds in which the airconditioning system is operated in DEMIST mode wherein the foot ventdoor 13 and the defroster door 14 are opened and the chest vent door 12is closed. During the DEMIST mode the compressor is controlled inaccordance with the routine shown in FIG. 13. This compressor controlwill be hereinafter referred to as a "low-temperature DEMIST control"because the control is effective under conditions of relatively lowambient temperature, that is, at the ambient temperature of the fourthstate shown at Step S706 of FIG. 6. In the "low-temperature DEMISTcontrol" mode, the compressor 2 is positively driven so as to providehigh dehumidification under high humidity and relatively low ambienttemperature, such as a rainy spell, in autumn or other high humidityconditions. As set forth, in this "low-temperature DEMIST control",frost tends to occur on the evaporator 4, thereby causing loweredefficiency of thermal exchange between the air flowing through theevaporator 4 and the refrigerant flowing in evaporator 4. Under thiscondition, if the compressor is driven for a long time, the refrigerantis not sufficiently evaporated, but a part of the refrigerant isliquefied, thereby causing damage to the compressor 2. Due to the frostadhering to the evaporator 4, the compressor 2 cannot be sufficientlycontrolled by the intake air temperature T_(INT) of the evaporator 4.Therefore, during the "low-temperature DEMIST control", the refrigeranttemperature T_(ref) and a target refrigerant temperature T'_(ref) areapplied as control parameters for the compressor control. The"low-temperature DEMIST control" begins at Step 7180 (S7180) and thenStep 7181 (S7181) proceeds in which a first target refrigeranttemperature T'_(ref1) is set to T_(AM) +T₈ (the ambient temperatureT_(AM) plus a predetermined temperature T₈, for example 16° C.) and asecond target refrigerant temperature T'_(ref2) is set to T_(AM) -T₉(the ambient temperature T_(AM) minus a predetermined temperature T₉,for example 4° C.) and further in which timers TIMER2 and TIMER3 are setto predetermined times t₂, for example 3 minutes and t₃, for example 2minutes respectively.

In Step 7182 (S7182), a test is made to determine whether a flag 1 inthe CPU is "0". If the answer to Step S7182 is in the affirmative, Step7183 (S7183) proceeds in which a test is made to determine whether aflag 2 in the CPU is "0". If the answer to Step S7183 is in theaffirmative, Step 7184 (S7184) proceeds in which the timer TIMER2 startsand then Step 7185 (S7185) proceeds in which the second targetrefrigerant temperature T_(ref2) is selected as a target refrigeranttemperature T'_(ref). Subsequently, in Step 7186 (S7186), the solenoidcurrent I_(SOL2) control is executed according to the procedure of FIG.14. This procedure of the solenoid current I_(SOL2) control is similarto that of the solenoid current I_(SOL1) control shown in FIG. 8. Theformer is different from the latter in a point that the temperaturesT_(INT) and T'_(INT) are replaced with the temperatures T_(ref) andT'_(ref), respectively. That is to say, in the solenoid current I_(SOL2)control, the solenoid current I_(SOL2) is derived on the basis of therefrigerant temperature T_(ref) and the target refrigerant temperatureT'_(ref). As set forth above, since the procedure of the solenoidcurrent I_(SOL2) control is similar to that of the solenoid currentI_(SOL1) control, a description has been omitted for the purpose of thesimplification of the disclosure. Likewise, in FIGS. 14A and 14B, thevalues of current I₁ and I₂, and the values of temperature T₂, T₂₁, andT₂₂ are respectively, for example 0.98 mA, 0.8 A, 6° C., -5° C. and 15°C. and these values are experimentally determined so as to suitablyoperate the solenoid 345.

Subsequently, in Step 7187 (S7187), a test is made to determine whetherthe preset time t₂ of the timer TIMER2 has elapsed. If the answer toStep S7187 is in the negative, Step 7194 (S7194) proceeds in which theflag 1 is set to "1" and the routine returns to the predeterminedprocedure. If the answer to Step S7187 is in the affirmative, Step 7188(S7188) proceeds in which the flag 1 is set to "0" and then Step 7189(S7189) proceeds in which the timer TIMER3 starts. Next, in Step 7190(S7190), the target refrigerant temperature T'_(ref1) is selected as thetarget refrigerant temperature T'_(ref) and then Step 7191 (S7191)proceeds in which the solenoid current I_(SOL2) control is executed asit is at Step S7186. Furthermore, in Step 7192 (S7192), a test is madeto determine whether the preset time t₃ of the timer TIMER3 has elapsed.If the answer to Step S7192 is in the negative, Step 7195 (S7195)proceeds in which the flag 2 is set to "1" and then the routine returnsto the predetermined procedure. If the answer to Step 7192 is in theaffirmative, Step 7193 (S7193) proceeds in which the flag 2 is set to"0" and then the routine returns to the predetermined procedure. That isto say, the procedure returns from Steps S7193, S7194, or S7195 to Step80 of FIG. 5.

As will be clearly seen from FIG. 13A, when the procedure of the"low-temperature DEMIST control" is executed, the target refrigeranttemperature T'_(ref2) and T'_(ref1) are selected by turns in accordancewith the elapse of the predetermined times t₂ and t₃. The elapse of thepredetermined time t₂ corresponds to Steps S7184 to S7187, while theelapse of the predetermined time t₃ corresponds to Steps S7189 to S7192.Therefore, the solenoid current I_(SOL2) is also changed in response tochange in the target refrigerant temperature T'_(ref), thereby causingthe pulsation of the compressor 2. In this manner, even if the flow ofrefrigerant is small, the lubricating ability of the compressor 2 isincreased, thereby preventing the compressor 2 from seizing.Furthermore, by the suitable selection of the preset times t₂ and t₃,dry air with a relatively low temperature is discharged through the footvent 7d and the defroster nozzle 7e to the passenger's feet and theinner surface of the front window. In this way, the suitabledehumidification is accomplished.

Moreover, in Step S716 of FIG. 6, the ambient temperature T_(AM) is inthe fifth state, Step 719 (S719) proceeds in which the compressor 2 isstopped and then the procedure returns to Step 80 of FIG. 5.

As will be appreciated from the above, although in the presentembodiment according to the invention, a swash-plate type of compressoris used for a variable displacement compressor, an inclined shaft typeof compressor may be used as a variable displacement compressor.

Although the discharge of a variable displacement compressor iscontrolled in such a manner that, when the suction pressure of thecompressor exceeds the preset pressure, the discharge of the compressoris increased, and conversely when the suction pressure of the compressoris lower than the preset pressure, the discharge of the compressor isdecreased, the discharge of the compressor may be controlled bycomparing the refrigerant temperature with a preset refrigeranttemperature as described in the above mentioned "low-temperature DEMISTcontrol".

While the foregoing is a description of the best mode for carrying outthe invention, it will be understood that the invention is not limitedto the particular embodiments shown and described herein, but mayinclude variations and modifications without departing from the scope orspirit of this invention as defined by the following claims.

What is claimed is:
 1. An automatic air conditioning system forautomotive vehicles with a variable displacement compressorcomprising:first detecting means for detecting an intake air temperaturedefined by a temperature of air flowing through an evaporator of saidair conditioning system placed just behind said evaporator; dischargechanging means for essentially changing the discharge volume ofrefrigerant discharged from said compressor on the basis of thedifference between said intake air temperature and its target value;mode signal generating means for generating a mode signal representingwhether said air conditioning system is operated in a first mode whereinconditioned air is simultaneously discharged from both of upper andlower discharge outlets or is operated in a second mode whereinconditioned air is discharged from either the upper or lower of saiddischarge outlets; and target value deriving means for deriving saidtarget value of said intake air temperature on the basis of said modesignal in such a manner that said target value in said first mode issmaller than said target value in said second mode.
 2. An automotive airconditioning system for automotive vehicles as set forth in claim 1,wherein said discharge changing means operates in such a manner that,when said intake air temperature is higher than said target value, thedischarge volume is essentially increased, and when said intake airtemperature is lower than said target value, the discharge volume isessentially decreased.
 3. An automatic air conditioning system forautomotive vehicles as set forth in claim 1, further comprising:seconddetecting means for detecting a physical quantity indicative ofenvironmental condition in and around the automotive vehicle; andcalculating means for calculating a target discharge air temperature, tobe discharged from said discharge outlets, on the basis of said physicalquantity and a preset temperature input from temperature setting meansfor setting a desirable room temperature in the vehicular cabin.
 4. Anautomatic air conditioning system for automotive vehicles as set forthin claim 3, wherein said physical quantity is ambient temperature,magnitude of insolation, and/or room temperature in the vehicular cabin.5. An automatic air conditioning system for automotive vehicles as setforth in claim 4, wherein said target value deriving means appropriatelyselects said target value of said intake air temperature in accordancewith said target discharge air temperature.
 6. An automatic airconditioning system for automotive vehicles comprising:discharge meansfor compressing and discharging refrigerant; discharge changing meansfor changing discharge volume of the refrigerant discharged from saiddischarge means; mode signal generating means for generating a modesignal representing whether said air conditioning system is operated ina first mode wherein conditioned air is simultaneously discharged fromboth upper and lower discharge outlets or is operated in a second modewherein conditioned air is discharged from either the upper or lower ofsaid discharge outlets; first detecting means for detecting an intakeair temperature defined by a temperature of air flowing through anevaporator of said air conditioning system placed just behind saidevaporator; second detecting means for detecting a physical quantityindicative of environmental conditions in and around the automotivevehicle; calculating means for calculating a target discharge airtemperature, to be discharged from said discharge outlets, on the basisof said physical quantity and a preset temperature input fromtemperature setting means for setting a desirable room temperature inthe vehicular cabin. target value deriving means for deriving anindividual target value of said intake air temperature in accordancewith said target discharge air temperature in such a manner that saidtarget value in said first mode is smaller than said target value insaid second mode; and control means capable of controlling saiddischarge changing means on the basis of the difference between saidintake air temperature and said target value in such a manner that, whensaid target value is lower than said intake air temperature, thedischarge volume of said discharging means is essentially increaseddepending on the difference, and when said target value is higher thansaid intake air temperature, the discharge of said discharging means isessentially decreased depending on the difference.
 7. An automatic airconditioning system for automotive vehicles as set forth in claim 6,wherein said physical quantity is ambient temperature, magnitude ofinsolation, and/or room temperature in the vehicular cabin.